Assessment of product composition and energy output of sewage sludge gasification by simulation model

Processing sewage sludge presents a significant challenge, necessitating concerted efforts to transform this waste into valuable resources such as syngas and biochar, which can be utilized across energy, chemical, agricultural, and other sectors. This paper examines the continuous gasification of sewage sludge in an inert environment. A systematic analysis of various process parameters was conducted to evaluate their impact on overall system performance, with particular emphasis on optimizing syngas yield, enhancing hydrogen content in the syngas, and maximizing energy output. The analyses were performed using a rigorously developed simulation model implemented within the UniSim Design environment based on specific assumptions and conditions. This model enabled a comprehensive investigation of the interrelationships among process variables and their influence on key performance metrics. Based on the insights gained, targeted recommendations were formulated to improve the efficiency and output of the gasification process. Optimal parameters identified for the reference sewage samples include a pyrolysis temperature range of 700–800 °C, a gas shift reactor temperature of 900–1000 °C, a feed water content of 8 % (by mass), and a slag recycle ratio of 0.8 (by mass) resulting to maximum yield of syngas of 46 % (by mass). The simulation model was validated with various sludge samples from the literature, illustrating the diversity of optimal parameters. These recommendations are aimed at enhancing syngas yield, increasing the hydrogen fraction in the syngas, and achieving higher overall energy output, thus contributing to the optimization of the process. The findings of this study provide insights into the factors that affect process performance and lay the groundwork for further advancements in the production and utilization of syngas derived from sewage sludge as a feedstock.